The Optical Transport Network (OTN) is a standard framework for optical networks employing wavelength division multiplexing (WDM). The OTN makes it possible to accommodate different types of client signals and enables high-volume transmission. In an optical transmission system conforming to the OTN, client signals are contained or multiplexed in an optical transfer unit (OTU) frame of the OTN for transmission (see, for example, Japanese Laid-Open Patent Publication No. 2008-113394).
ITU-T G.709 defines the Asynchronous Mapping Procedure (AMP) that is a scheme to compensate for a difference between the bit rate of a frame signal and the bit rate of a signal to be contained in the frame signal. In the AMP, a signal (hereafter called a “constituent signal”) to be contained in a frame signal is asynchronously mapped to the frame signal to compensate for the difference in the bit rates. ITU-T G.709 also defines the Generic Mapping Procedure (GMP) for mapping constituent signals having high and various bit rates. In the GMP, the number of data entities and the number of stuff bytes to be contained in an area of a frame are calculated based on the difference in the bit rates between the constituent signal and the frame signal, and the constituent signal is mapped to the frame signal to compensate for the difference in the bit rates.